Re: [PATCH v2] mm/slub: preserve original size in _kmalloc_nolock_noprof retry path

[Vlastimil Babka (SUSE)]

On 6/4/26 14:27, hu.shengming@xxxxxxxxxx wrote:
> From: Shengming Hu <hu.shengming@xxxxxxxxxx>
> 
> _kmalloc_nolock_noprof() retries from the next kmalloc bucket when the
> initial allocation fails. The retry currently reuses `size` as the
> bucket selector and overwrites it with s->object_size + 1.
> 
> That value is later passed as the original allocation size to
> __slab_alloc_node(), slab_post_alloc_hook() and kasan_kmalloc(). On a
> successful retry this makes KASAN/slub-debug observe the retry bucket
> selector rather than the caller requested size, potentially widening the
> valid kmalloc range and hiding overflows.
> 
> Keep the caller requested size separately as orig_size and pass it to
> the allocation/debug/KASAN paths. Continue using `size` as the retry cache
> selector.
> 
> Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock()")
> Signed-off-by: Shengming Hu <hu.shengming@xxxxxxxxxx>

Merged to slab/for-next, thanks!

> ---
> Changes in v2:
> - Use an explicit orig_size variable instead of bucket_size, as suggested
>   by Harry and Vlastimil.
> - Link to v1: https://lore.kernel.org/all/20260603211011530GqLSXP_rgcuQdR47IGQLL@xxxxxxxxxx/
> 
> ---
>  mm/slub.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 67abbbf68fc1..7e1a1fe5daaa 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5350,6 +5350,7 @@ EXPORT_SYMBOL(__kmalloc_noprof);
>  void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, int node)
>  {
>  	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_NOMEMALLOC | gfp_flags;
> +	size_t orig_size = size;
>  	struct kmem_cache *s;
>  	bool can_retry = true;
>  	void *ret;
> @@ -5398,7 +5399,7 @@ void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, in
>  	 * kfence_alloc. Hence call __slab_alloc_node() (at most twice)
>  	 * and slab_post_alloc_hook() directly.
>  	 */
> -	ret = __slab_alloc_node(s, alloc_gfp, node, _RET_IP_, size);
> +	ret = __slab_alloc_node(s, alloc_gfp, node, _RET_IP_, orig_size);
> 
>  	/*
>  	 * It's possible we failed due to trylock as we preempted someone with
> @@ -5422,9 +5423,9 @@ void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, in
>  success:
>  	maybe_wipe_obj_freeptr(s, ret);
>  	slab_post_alloc_hook(s, NULL, alloc_gfp, 1, &ret,
> -			     slab_want_init_on_alloc(alloc_gfp, s), size);
> +			     slab_want_init_on_alloc(alloc_gfp, s), orig_size);
> 
> -	ret = kasan_kmalloc(s, ret, size, alloc_gfp);
> +	ret = kasan_kmalloc(s, ret, orig_size, alloc_gfp);
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(_kmalloc_nolock_noprof);